A sheet processing apparatus set adjacent to an image forming apparatus receives a recording medium subjected to image formation from the image forming apparatus and performs stapling and saddle folding.
The processing speed of the sheet processing apparatus is lower than the image forming speed of the image forming apparatus. The sheet processing apparatus includes, in order to absorb this speed difference, a waiting tray on which plural recording media received from the image forming apparatus are temporarily stacked and a processing tray configured to receive the recording media from the waiting tray and align the recording media before stapling is performed.
The sheet processing apparatus stacks the plural recording media received from the image forming apparatus on the waiting tray and, when stapling of preceding recording media ends, drops following recording media from the waiting tray to the processing tray.
The sheet processing apparatus aligns the recording media received by the processing tray using a lateral alignment device and a longitudinal alignment device.
The longitudinal alignment device includes a paddle set above the processing tray and configured to strike down the recording media and draw in the recording media to bump the recording media against a stopper and a longitudinal alignment roller configured to convey the stacked recording media to bump the recording media against the stopper.
The paddle is formed of a flexible material. The recording media received from the image forming apparatus are heated. Therefore, in the sheet processing apparatus in the past, the paddle is softened by the heat of the recording media and an alignment failure of longitudinal alignment occurs.
An aligning ability of the longitudinal alignment roller is higher as the longitudinal alignment roller rotates faster. However, if the number of revolutions of the longitudinal alignment roller is excessively increased when frictional force on surfaces of the recording media is small, a slip occurs and an alignment failure of longitudinal alignment occurs.
The paddle of the sheet processing apparatus in the past is set in a place deviating from a place right above the longitudinal alignment roller. Therefore, a grip of the recording media by the paddle and the longitudinal alignment roller is weak and an alignment failure of longitudinal alignment occurs.
Therefore, there is a demand for a sheet processing apparatus and a sheet processing method that can accurately perform longitudinal alignment irrespective of a degree of friction on the surfaces of recording media and even if a paddle is softened by the heat of the recording media.